Selenium and Tellurium Toning

[LF_rookie_to_be]

Hopefully the moderators won't remove this thread for copyright infringement and leave it for why it's here - sheer informational and, perhaps, historical value to everyone with no access to the source (Haist). Enjoy the read.


Selenium and Tellurium Toning

Sulfur, selenium, and tellurium are members of the same family of elements. Selenium and tellurium, as does sulfur, combine with silver to form brown-colored deposits of great stability. The use of sulfur (hydrogen sulfide) for brown-toning the photographic image was mentioned by W. H. Fox Talbot in 1849. On the other hand, tellurium, which forms a reddish-brown color with silver, is of more recent origin for toning silver images, having been first used by T. Thorne Baker in 1901. And toning of the silver image with selenium was first disclosed in a patent in 1910 (German Patent 238,513 of Rheinische Emulsions-Papier-Fabrik Akt.-Ges. in Dresden).
Selenium and tellurium are difficult to solubilize. The early patents, as reviewed by Karl Kieser, are concerned with methods of preparing suitable solutions of selenium or tellurium. The first patent (German Patent 238,513) on a selenium toning bath formed the toning solution by dissolving 10 g of metallic selenium in 100 g of sodium sulfide in 500 ml of water, then making the solution to a volume of one liter. Ammonium sulfide, other sulfides, or polysulfide may be used in place of the sodium sulfide. If the highlight areas of the image were tinted with stain, the coloration could be removed by treating the image with a solution of 10% sodium bisulfite.
As A. Sedlaczek has pointed out, however, "The known solution of selenium or selenium compounds in alkali sulphide is, however, subject to certain disadvantages, in that it attacks the skin, smells unpleasantly, and quickly deteriorates on diluting. These disadvantages are claimed to be removed by sulphite. The sulphite-containing solution has no odour, has little action on the skin, and is stable upon exposure to air. The following example is specified: 1 gm. (9 grs.) of metallic selenium is dissolved by boiling in a solution of 10 gms. (88 grs.) of sodium sulphide in 50 gms. (1 oz.) of water and the resulting solution is poured into 1,000 c.c.s. (20 ozs.) of a 20 percent solution of sodium sulphite (German Patent No. 335,627 by the Chem. Fabrik auf Aktien, vorm. E. Schering, of Berlin)." Reddish-brown image tones were obtained when fixed and well-washed prints were treated in the bath. Stained highlights may occur, requiring immersion in potassium metabisulfite solution to clear the stain.
Other methods were quickly patented for forming selenium toning baths. (Generally, the same techniques were applied to solubilizing tellurium, but the solutions were not as satisfactory.) Sodium selenosulfate in combination with sodium sulfite and sodium thiosulfate formed the toning bath disclosed in 1912 (German Patent 280,679). Selenious acid in hydrochloric acid solution was also patented (German Patent 283,205) as a toning bath. Following a study of various selenium toning solutions, Jaroslav Milbauer expressed a preference for the use of sodium sulfide and selenious acid.

[LF_rookie_to_be]

Many of the methods for preparing toning baths with selenium (or tellurium) involve the use of sodium sulfide or sodium sulfite. Selenium, for example, undergoes many of the same reactions of sulfur, such as

Na₂S + S --> Na₂S₂

Na₂S + Se --> NaSeS

or

sodium sulfite + sulfur --> sodium thiosulfate

sodium sulfite + selenium --> sodium selenosulfate

Sodium selenosulfide, NaSeS, or sodium selenosulfate, NaSeSO₃, are believed to be the active toning agents in many selenium toning solutions. When sodium selenite is dissolved in sodium sulfite-sodium thiosulfate solutions, the selenosulfate is probably the toning agent.
A. Seyewetz has commented as follows upon the two types of selenium toning solutions:

"Selenium which has been dissolved in a solution of sulphide or in one of an alkaline sulphite forms solutions which allow of changing the colour of the image on chloro-bromide development papers from its original black gradually to warm brown and thence to sepia.
These two kinds of solutions modify the colour of silver images in the same way, although they contain very different selenium compounds. That prepared with sulphite is colourless and probably consists of a solution of sodium selenosulphate dissolved in excess of alkaline sulphite. That made with sulphide is of brownish red colour and has the composition of an alkaline selenosulphide, analogous to a bisulphide.
These two methods of selenium toning exhibit, however, marked differences in their action.
While both of them behave similarly in modifying the colour of prints on chloro-bromide papers, the solution of seleno-sulphide is for toning prints on bromide papers by the two-bath method, viz., by bleaching the image to silver bromide by a mixture of ferricyanide and bromide before treating it with alkaline sulphide or seleno-sulphide. Moreover the two kinds of solutions, when in a diluted condition, have very different keeping qualities. The seleno-sulphate solution is stable but the seleno-sulphide, when diluted, undergoes hydrolysis very rapidly, selenium being precipitated."

[LF_rookie_to_be]

It is thought that the toning action of selenosulfate (formed by the reaction of selenium in sodium sulfite solution) with silver of the image involves the reaction

sodium selenosulfate + silver --> silver selenide + sodium sulfite

Sodium selenosulfide (formed when selenium is solubilized in sodium sulfide
solution) reacts with the silver of the image to form silver selenide as well.

Na₂SeS + 2 Ag --> Ag₂Se + Na₂S

Either of the two primary selenium toning solutions produces the same silver compound. The absence of silver in used selenium toning baths would indicate that there is no passage of silver into solution. Seyewetz analyzed the toned silver images formed by using either sodium selenosulfide or sodium selenosulfate. He concluded, "The quantity of selenium corresponding with 100 gms. silver in silver selenide Ag₂Se is 36.6 gms., and it is therefore evident that the composition of the toned image is very near to that of this silver selenide and is practically the same in the two different methods of toning." The ratio of silver to selenium in the final toned image is higher for chloride papers than for bromide papers. It has been suggested "that silver selenide (as obtained on bromide papers) is black, and that any reddish-brown tone produced on other papers is due to the deposition of elemental red selenium in the image in addition to the black silver selenide."

[LF_rookie_to_be]

(...)

[LF_rookie_to_be]

Present-day selenium toners do not differ greatly from the early formulations. The actual toning agent is not available as a separate chemical but may be prepared by dissolving selenium metal in sodium sulfite or sodium sulfide solution. (Note: Powdered selenium metal is very poisonous, and breathing the powder must be avoided. Contamination of breaks in the skin with either the powder or solution should also be avoided.)
Two formulations for selenium toning are the Selenium Toner T-55 and the sulfide-selenium toner T-56 of Kodak, Limited (London). The Kodak T-55 toner may be used for chlorobromide and bromide photographic papers; the T-56 toner, which involves a two-step, bleach-and-tone procedure, is recommended for chloride and other photographic papers that do not tone satisfactorily in the T-55 toner.

Kodak Selenium Toner T-55: Stock Solution

Hot water - 700 ml
Sodium sulfite, desiccated - 150 g
Selenium metal, powdered - 6 g
Ammonium chloride - 190 g
Cold water to make - 1 liter

Dissolve the sodium sulfite in about 700 ml of hot water, add the selenium, and boil for about 30 min. If the solution still has some residue, filter the solution to remove any residue. The solution is allowed to cool before adding the ammonium chloride. Add cold water to make one liter of toning stock solution.
For use, add five parts of water to one part of the stock solution.
Prints should be thoroughly washed after fixing; preferably, two-bath fixation should be used to remove all silver thiosulfates as well as the thiosulfate. Immerse the print in the toning bath for 10 to 15 min, 68°F (20°C). Wash thoroughly before drying the print.
The T-55 toner, according to the Photo-Lab Index, is available in the United States as Kodak rapid selenium toner and in England as Kodak selenium toner. Commercial preparations of selenium toners often involve sodium selenite, rather than metallic selenium, combined with sodium sulfite and a thiosulfate, particularly the ammonium salt, because the solution is less hazardous to prepare and more rapidly mixed.

[LF_rookie_to_be]

The Kodak sulfide-selenium toner T-56 is a toning bath for difficult-to-tone photographic papers, involving a first solution to bleach the silver image followed by a selenium toning bath. These solutions have the following composition:

Kodak Sulfide-Selenium Toner T-56

Solution A: Bleaching Bath

Potassium ferricyanide - 50.0 g
Potassium bromide - 50.0 g
Cold water to make - 1.0 liter

Solution B: Toner Stock Solution

Warm water (125°F or 52°C) - 750.0 ml
Sodium sulfide, pure crystals - 250.0 g
Selenium powder - 5.7 g
Cold water to make - 1.0 liter

The thoroughly washed print is bleached in solution A, then washed in running water until the yellow stain is removed. The print is then placed in a toning solution consisting of one part of solution B and 20 parts of water. When the image is completely formed again, wash the print in running water and then dry without heating.

[LF_rookie_to_be]

The selenium toner, says Ansel Adams, is "the only toner I use." The Adams selenium toner has the following composition:

Selenium Toner (Ansel Adams)

Solution A

Boiling water - 250.0 ml
Sodium sulfide, crystals - 60.0 g
Selenium metal, powdered - 5.5 g

Solution B

Water (125°F) - 3000.0 ml
Sodium thiosulfate, crystals - 660.0 g

Add solution A to solution B. Then

Dissolve sodium bisulfite - 210.0 g
Add water to make - 4000.0 ml

Cool to 75°F before use.

Ansel Adams offers some practical suggestions that might be applied to all selenium toning operations. Develop the print fully, fix in at least two fixing baths, and wash thoroughly. The print, wet or dry, should then be immersed for 15 to 30 sec in a 2 % Kodalk solution, a procedure that this writer also has followed for some years. The print is then rinsed with water and put in a separate tray of water for holding until ready for toning. Tone with constant agitation, carrying the shade of the wet print a little beyond the desired point. Rinse the toned print with water and then wash for at least 1 hr. Dry the print naturally, without heat, if possible.
As with sulfur toning, there has been a considerable quantity of research on selenium toning, resulting in a number of variations in the toning solution or procedure. An extensive review of selenium toning methods has been written by E. Asloglou. Felix Formstecher has written on the history and theory of the process. Many of the improvements in selenium toning have been the result of industrial research, resulting in a number of patents.

[paulr]

Interesting, especially on tellurium. That's a new one for me. Have you used it, or seen the results? I wonder how it would work in combination with selenium ... possibly a bit of warmth to offset the selenium's cooler tones.

[bob carnie]

I find selenium warm towards red, not cool.

Interesting, especially on tellurium. That's a new one for me. Have you used it, or seen the results? I wonder how it would work in combination with selenium ... possibly a bit of warmth to offset the selenium's cooler tones.

[Mark Sampson]

Tellurium? Is that a radioactive element? Seems like a pretty sketchy idea if it is. I've seen references to uranium toning, which, like mercury intensification, makes me think that people would try anything, no matter how dangerous.